It has been known that optical characteristics of various optical elements and semiconductor thin film forming processes can be evaluated using an ellipsometer which irradiates an object under measurement with light and measures a state of polarization from light reflected or transmitted by the object under measurement (for example, see JP-A-2004-294370).
There are several methods for measurement using an ellipsometer, including measuring techniques referred to as rotary polarizer method, rotary analyzer method, and rotary compensator method. Those measuring techniques involve the step of rotating a polarizer, an analyzer, and a compensator, respectively, and resultant states of polarization of light entering or exiting those elements are measured. According to any of those techniques, data are acquired at each predetermined angle, a half rotation of the polarizer, analyzer, or compensator serving as one unit of angle. The state of polarization of an object under measurement is calculated from data of the quantity of light measured at each predetermined angle.
The above-mentioned measuring method will now be briefly described.
As exemplified in FIG. 8, a measuring system according to the rotary polarizer method includes a light source 101 such as a semiconductor laser, a polarizer 102 forming linearly polarized light in an arbitrary direction, a sample 103 that is an object under measurement, an analyzer 104, and a light-receiving device 105 for receiving light transmitted through the analyzer 104. The polarizer 102 is accompanied by a rotary mechanism for changing the polarization direction, and the rotary mechanism includes a first pulley 106B secured on an output shaft off a motor 106A and a second pulley 106D which is connected to the first pulley 106B through an endless belt 106C and on which the polarizer 102 is rotatably mounted. Light from the light source 101 passes through the polarizer 102 and impinges upon the sample 103, and light transmitted by the sample 103 is measured by the light-receiving device 105 through the analyzer 104. The polarization direction of the polarizer 102 is varied by rotating the polarizer with the motor 106A to vary the polarization direction of light incident on the sample 103. As a result, the amount of transmitted light in each polarization direction is identified by the light-receiving device 105, which makes it possible to measure polarization characteristics of the sample 103.
As exemplified in FIG. 9, a measuring system according to the rotary analyzer method includes a light source 101 such as a semiconductor laser, a polarizer 102 forming linearly polarized light in a particular direction, a sample 103, an analyzer 104 forming linearly polarized light in an arbitrary direction, and a light-receiving device 105 for receiving light transmitted through the analyzer 104. This configuration provides a measuring system in which the rotary mechanism accompanying the polarizer 102 shown in FIG. 8 is provided on the analyzer 104 instead of the polarizer 102. In this system, light transmitted through the sample 103 is split into components in some polarization directions to measure the state of polarization.
According to the rotary compensator method, as exemplified in FIG. 10A, a measuring system includes a light source 10 such as a semiconductor laser, a polarizer 102 forming linearly polarized light in a particular direction, a sample 103, an analyzer 104 for detecting the state of polarization, and a light-receiving device 105 for receiving light transmitted through the analyzer 104. The measuring system further includes a compensator 107 which is rotatably supported midway the optical path between the polarizer 102 and the sample 103. The compensator 107 is driven for rotation by a rotary mechanism as shown in FIG. 8, and the state of polarization of light radiated to the sample is varied accordingly. At this time, the state of polarization of light transmitted through the sample 103 varies as the compensator 107 is rotated, and polarization characteristics of the sample 103 are measured by detecting the state of polarization at the light-receiving device 105 through the analyzer 104. According to the rotary compensator method, as shown in FIG. 10B, a measuring system may alternatively be provided, in which the compensator 107 is provided midway the optical path between the sample 103 and the analyzer 104.